200 Intelligence and Miscellaneous Articles. 



The intrusive rocks are mostly dolerites, consisting chiefly of 

 augite and plagioclase (labradorite-andesine), without olivine or 

 rhombic pyroxenes. Epidote is very abundant as an alteration- 

 product. Contemporaneous veins are met with at one locality. 

 Small intrusions of eurite occur just beyond the limits of the map. 



The rhyolites are sometimes compact, sometimes banded, and 

 sometimes nodular. Analyses of two specimens, the one compact 

 and the other nodular, show that the percentage of soda is high. 



The tuffs or ashes vary considerably in character. Some consist 

 of a fine matrix with numerous scattered angular fragments of all 

 sizes up to 18 inches ; the fragments are mostly rhyolitic, but 

 pieces of slate and grit also occur. In others the fragments are 

 smaller, and some are so finely laminated that on freshly broken 

 surfaces the texture appears perfectly uniform, but on weathered 

 surfaces the lamination is often quite distinct. 



Andesitic lavas occur at two horizons, in the Upper Lingular 

 Flags and in the Llandeilo Series. The latter are often highly 

 amygdaloidal. 



The Rhyolitic Series appears to be older than the main mass of 

 volcanic rocks in the Arenig area, but it may be contemporaneous 

 with the Calymene Ashes of that district. It is probably of 

 approximately the same age as the volcanic series of Skomer 

 Island, and the fact that in both places the rhyolitic rocks are 

 soda-rhyolites is of considerable interest. 



2. ' Insect-Remains from the Midland and South-Eastern Coal- 

 fields.' By Herbert Bolton, E.R.S.E., F.G.S., Director of the 

 Bristol Museum. 



XXIV. Intelligence and Miscellaneous Articles. 



Trinity College, 



Cambridge. 

 November 25th, 1912. 



To the Editors of the Philosophical Magazine, 

 Gentlemen, — 



IN my paper, "The Relation of Airy's Integral to the Bessel 

 Functions," published in the Phil. Mag. for July 1909, there 

 is a numerical error which I wish to correct. Equation (40) on 

 page 15 is inaccurate, so that the Table on page 16 gives the 

 values not of 2-1123(>-z)/zt, but of V 3447 (n-z)/zh 



Tours very truly, 



J. W. Nicholson, 



